North Carolina revises wheat recommendations

Feb 24, 2010

North Carolina State University and the North Carolina Department of Agriculture and Consumer Services are advocating a new approach for deciding how much nitrogen to put out on wheat.

The revised guidelines take into account crop biomass and often call for significantly less nitrogen than previous recommendations. Growers lucky enough to have a stand, despite the poor planting conditions last fall, may be able to use the new guidelines to reduce input costs without compromising yield.

Split applications of nitrogen are likely to be necessary this year, said Ben Knox, NCDA&CS regional agronomist. The first step in determining nitrogen needs involves a tiller count at green up.

“If the tiller count is low, growers should put out some nitrogen as soon as possible,” Knox said. “If there are fewer than 50 tillers per square foot of row, growers need to apply up to half (about 60 pounds) of the spring nitrogen now. For counts between 50 and 70 per square foot, 30 to 40 pounds of nitrogen should be applied. If the tiller count is high, but the wheat is yellow, an application of 30 pounds of nitrogen is appropriate.

“I have seen fields with as few as 15 to 20 tillers per square foot at this time of year end up making good wheat,” Knox said. “A timely nitrogen application followed by some dry weather and warm temperatures can yield surprising results. However, even if the wheat is thin and has to be abandoned, the nitrogen will not have been wasted. It will have made the wheat a better cover crop.”

After an early nitrogen application, growers will need to wait until Zadok’s growth stage 30 (GS-30) to implement the new guidelines to determine how much additional nitrogen is necessary.

To make that determination, North Carolina growers must collect two types of samples: A tissue sample and a matching above-ground biomass sample. Each pair of these samples should be given the same sample ID and be submitted to the NCDA&CS Agronomic Division laboratory within 24 hours of collection.

In the past, North Carolina growers relied on recommendations developed in Virginia that are most reliable for wheat grown on well-drained soils. By taking into account biomass measurements , the new recommendations detect and account for differences in crop growth, such as those due to planting date, row spacing and moisture levels. Considering the extraordinary amount of rain North Carolina has experienced this fall and winter, the new system should prove to be particularly valuable for determining Wheat normally reaches GS-30 any time from mid-February to mid-March, depending on variety, planting date and environmental conditions. When plants begin to stand up straight, growers should try to verify that a crop is at GS-30 by pulling up several plants, splitting the stems from the top to the base, and looking for the growing point. Prior to GS-30, the growing point will be just above the roots; at GS-30, it will have moved about one-half inch up the stem.

At GS-30, tissue sampling involves cutting 20 to 30 plants about one-half inch above the ground from representative areas throughout a field. In general, two large, fistfuls of leaves make a good sample. Dead leaves and weeds should be Biomass samples, on the other hand, should contain all the above-ground wheat-plant tissue from one, representative, 36-inch section of row. In broadcast fields where there are no rows, growers should collect all the plants from one square yard. In either case, soil and weeds should be carefully removed and the sample placed in a paper bag. Write the sample ID from the corresponding tissue sample and the word “biomass” on the bag.

Upon receiving an NCDA&CS Plant Analysis Report, growers should first look for the biomass and N% values . Randy Weisz of North Carolina State University has developed a couple of interpretive tools that use these values to determine an appropriate nitrogen rate.